1. Field of the Invention
This invention relates a process for the removal of a dissolved metallic catalyst from a crude ester product. More specifically, the invention relates to a process for removal of residual soluble tin catalyst from the crude product in an organic ester synthesis.
2. Statement of Related Art
Organic esters and, in particular, carboxylic acid esters such as fatty acid esters, have widespread applicability in industry. For instance, they are widely used as surfactants in cleaning preparations; as base stocks for synthetic lubricants; as foam inhibitors both in the preparation of polymers (such as polyurethanes) and in the food industry for production of sugar-based products such as molasses or yeast and enzyme-based products such as beer; and in the production of phosphoric acid from mineral phosphates.
Carboxylic acid esters in general, and fatty acid esters in particular, are normally prepared in the presence of a catalyst to reduce reaction time and/or to increase the yield. For instance, insoluble tin powder or titanic acid esters have been employed as catalysts in the preparation of fatty acid esters. After such an esterification reaction is completed, it is desirable to remove the esterification catalyst, for example by simple filtration, if the catalyst is insoluble in the esterification reaction mixture.
In other instances, however, a soluble metallic catalyst, such as a tin salt, is used, which may not be completely removed simply by filtration. While it may be tried to remove these soluble compounds from the crude fatty acid ester product by distillation, such a procedure is expensive, time consuming and relatively ineffective. Moreover, distillation may be damaging to some fatty acid esters which cannot withstand the required heat, and ineffective in removing others having high boiling points.
It has also been tried to use certain absorbent materials as a post-treatment step to remove catalyst. Such known methods, too, are expensive and time consuming, and achieve unsatisfactory levels of catalyst removal.